Shuttle Radar Topography Mission Digital Elevation Model Data Research Articles

Sustainability Evaluation of the Al-Qasab Playa by Integrating Hydrogeochemical and Graphical, ArcGIS Watershed, and Thermodynamic Geochemical Modeling Approaches

Drawing development plans requires evaluating the available resources and assessing their sustainable and subsequent utilization-driven environmental impacts. The current work is concerned with evaluating the sustainability of the halite harvesting process from Al-Qasab Playa, Shaqra, Central Saudi Arabia. The authors integrated, conceptually and quantitatively, ArcGIS-processed SRTM-DEM (Shuttle Radar Topography Mission-Digital Elevation Model) data, hydrogeochemical and thermodynamic-based geochemical modelling, and graphical approaches to achieve the ultimate aims of the study. The watershed is identified as a nonmarine closed basin with a drainage area of 1290 km2, with the slope controlling recharge to the Playa. The Chadha plot including the rainwater exhibits linear regression, with an R2 value of 0.9947, confirming the rainwater origin of the Playa water. The hardness-forming ions are primarily removed in pond 3, eliminating the need for costly and power-consuming steps of softening with ion exchange resins or nanofiltration as it can be used directly as a readily available feed for the chlor-alkali process for producing NaOH, Cl2, and H2 gases through electrolysis. XRD (X-ray diffraction) analysis and the SEM-EDS (Scanning electron microscopy-energy dispersive X-ray spectroscopy) of the harvested halite confirmed its purity. An improved design of the current folkloric harvesting process has been proposed based on the saturation indices calculated thermodynamically to provide a readily available feed intake for the electrolysis chlor-alkali process with or without minimal pretreatment to produce higher value chemicals. The methodological aspects presented here are deemed robust and valid for applications in other study areas, including the assessment of the exploitation of the rejected brine from the desalination plants to achieve the zero liquid discharge approach, as well as other types of sabkhas, regardless of their geographical location.

Forest Canopy Height Estimation Using Polarimetric Interferometric Synthetic Aperture Radar (PolInSAR) Technology Based on Full-Polarized ALOS/PALSAR Data

Forest canopy height is a basic metric characterizing forest growth and carbon sink capacity. Based on full-polarized Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR) data, this study used Polarimetric Interferometric Synthetic Aperture Radar (PolInSAR) technology to estimate forest canopy height. In total the four methods of differential DEM (digital elevation model) algorithm, coherent amplitude algorithm, coherent phase-amplitude algorithm and three-stage random volume over ground algorithm (RVoG_3) were proposed to obtain canopy height and their accuracy was compared in consideration of the impacts of coherence coefficient and range slope levels. The influence of the statistical window size on the coherence coefficient was analyzed to improve the estimation accuracy. On the basis of traditional algorithms, time decoherence was performed on ALOS/PALSAR data by introducing the change rate of Landsat NDVI (Normalized Difference Vegetation Index). The slope in range direction was calculated based on SRTM (Shuttle Radar Topography Mission) DEM data and then introduced into the s-RVoG (sloped-Random Volume over Ground) model to optimize the canopy height estimation model and improve the accuracy. The results indicated that the differential DEM algorithm underestimated the canopy height significantly, while the coherent amplitude algorithm overestimated the canopy height. After removing the systematic coherence, the overestimation of the RVoG_3 model was restrained, and the absolute error decreased from 23.68 m to 4.86 m. With further time decoherence, the determination coefficient increased to 0.2439. With the introduction of range slope, the s-RVoG model shows improvement compared to the RVoG model. Our results will provide a reference for the appropriate algorithm selection and optimization for forest canopy height estimation using full-polarized L-band synthetic aperture radar (SAR) data for forest ecosystem monitoring and management.

European Digital Elevation Model Validation against Extensive Global Navigation Satellite Systems Data and Comparison with SRTM DEM and ASTER GDEM in Central Macedonia (Greece)

Digital elevation models (DEMs) are a widely used form of topographic information, with some of the most popular being the Shuttle Radar Topography Mission (SRTM) DEM and the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM). These two sources of topographical information are the main constituents of the European Union Digital Elevation Model (EU-DEM), which is a relatively new dataset of the EU’s Copernicus Land Monitoring Service. In this context, the purpose of this study was to validate EU-DEM for its vertical accuracy and to compare it with SRTM DEM and ASTER GDEM data. This was achieved in a Geographic Information System (GIS) environment, using extensive—in the order of tens of thousands of points—geodetic Global Navigation Satellite System (GNSS) measurements and appropriate pre-processing steps. The absolute elevation errors results had a Root Mean Square Error (RMSE) of 2.7 m at a 90% confidence level and characterize the performance of EU-DEM from local to regional scale, generally confirming that it is an enhanced source of elevation information when compared with its predecessors.

The role of pre-existing Precambrian structures in the development of Rukwa Rift Basin, southwest Tanzania

In this study, Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) and aeromagnetic data are used to analyse the trends of pre-existing basement structures within the Rukwa Rift Basin. The NW-trending Rukwa Rift Basin on the western branch of the East African Rift System, southwest Tanzania, is developing on the NW-trending Paleoproterozoic Ubendian orogenic belt, a belt that experienced multiple orogenic collisions associated with subduction in Proterozoic time and comprises several distinct terranes bounded by faults or shear zones. The results obtained using magnetic edge enhancement (derivatives) methods highlight major magnetic domains identified based on their distinctive magnetic patterns in relation to geology and tectonic setting of the studied area. The results also highlight the Precambrian Chisi shear zone which trends in a NW-SE direction in the subsurface, below the Lake Beds Formation sedimentary succession of the Neogene Rukwa Rift Basin. The orientation of rift border faults and other major faults and their relationship with basement fabrics inferred from SRTM DEM and magnetic data trend mainly NW-SE, which is consistent with those of the NW-trending Paleoproterozoic Ubendian orogenic belt. Thus, Paleoproterozoic Ubendian orogenic belt structures have played a significant role on geometry and orientation of the Rukwa Rift Basin. These structures facilitated strain localisation within the border faults of the rift basin by exploiting the existence of inherited lithospheric heterogeneity. It can be concluded that the pre-existing faults and shear zones define a mechanical anisotropy in the basement of the Rukwa Rift Basin and facilitated the strain localisation within the border faults of the rift.

Physical evolution of the Three Gorges Reservoir using advanced SVM on Landsat images and SRTM DEM data.

The Three Gorges Reservoir (TGR) is one of the largest hydropower reservoirs in the world. However, changes of the important physical characteristics of the reservoir covering pre-, during-, and post- dam have not been well studied. This study analyzed the lengths and water surface areas of the TGR using advanced support vector machine method (SVM) combined Landsat images with the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM), which showed an increasing trend of lengths and surface areas with variable growth rates from pre-dam period to post-dam period. The highest water level (ca. 171.5m) was reported in 1st Jan, 2015, with the longest length of 687.8km and largest water surface area of 1106.2km2 during the study period. The lowest increasing magnitude of the reservoir length occurred in the first stage (2000-2005) but with the fastest magnitude of water surface area increase. The third stage (2010-2015) showed highest increase magnitude of length and lowest increase magnitude of water surface area. Meanwhile, the increased reservoir areas were mainly from cultivated land, forest land, and building land, with the biggest increase rate of cultivated land regardless of periods. Specifically, cultivated land contributed 39.1-46.0% to increased reservoir water area; the proportions were 22.6-29.6%, 22.1-24.1%, and 5.6-9.4% for forest, building land, and grassland, respectively. The study provides important data for the TGR physical evolution in the Holocene.

A global corrected SRTM DEM product for vegetated areas

ABSTRACTIt has been found that the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) is systematically higher than the actual land surface in vegetated areas. This study developed a new globally corrected SRTM DEM through reducing its systematic bias in vegetated areas. Over 150, 000 km2 airborne light detection and ranging (LiDAR) data along with spaceborne LiDAR, global canopy height data, global canopy cover data and global land cover data were collected to correct the SRTM DEM. A linear regression based method was used to estimate the original SRTM DEM error and therefore correct the SRTM DEM data. The results show that the original SRTM DEM data is around 6 m higher than the actual land surfaces on average across all vegetation types. Our corrected SRTM DEM data can significantly reduce the significant bias to near zero, and can also reduce the root-mean-square error by 1 m.

Assessing groundwater accessibility in the Kharga Basin, Egypt: A remote sensing approach

We used multi-map analysis of remote sensing and ancillary data to identify potentially accessible sites for groundwater resources in the Kharga Basin in the Western Desert of Egypt. This basin is dominated by Cretaceous sandstone formations and extends within the Nubian Sandstone Aquifer. It is dissected by N-S and E-W trending faults, possibly acting as conduits for upward migration of groundwater. Analysis of paleo-drainage using Digital Elevation Model (DEM) generated from the Shuttle Radar Topography Mission (SRTM) data shows that the Kharga was a closed basin that might have been the site of a paleo-lake. Lake water recharged the Nubian Sandstone Aquifer during the wetter Holocene time. We generated the following layers for the multi-map analysis: (1) Fracture density map from the interpretation of Landsat Operational Land Imager (OLI), SRTM DEM, and RADARSAT data. (2) Thermal Inertia (TI) map (for moisture content imaging) from the Moderate Resolution Imaging Spectroradiometer (MODIS) data. (3) Hydraulic conductivity map from mapping lithological units using the Landsat OLI and previously published data. (4) Aquifer thickness map from previously published data. We quantitatively ranked the Kharga Basin by considering that regions of high fracture density, high TI, thicker aquifer, and high hydraulic conductivity have higher potential for groundwater accessibility. Our analysis shows that part of the southern Kharga Basin is suitable for groundwater extraction. This region is where N-S and E-W trending faults intersect, has relatively high TI and it is underlain by thick aquifer. However, the suitability of this region for groundwater use will be reduced significantly when considering the changes in land suitability and economic depth to groundwater extraction in the next 50 years.

Mapping CORINE Land Cover from Sentinel-1A SAR and SRTM Digital Elevation Model Data using Random Forests

The European CORINE land cover mapping scheme is a standardized classification system with 44 land cover and land use classes. It is used by the European Environment Agency to report large-scale land cover change with a minimum mapping unit of 5 ha every six years and operationally mapped by its member states. The most commonly applied method to map CORINE land cover change is by visual interpretation of optical/near-infrared satellite imagery. The Sentinel-1A satellite carries a C-band Synthetic Aperture Radar (SAR) and was launched in 2014 by the European Space Agency as the first operational Copernicus mission. This study is the first investigation of Sentinel-1A for CORINE land cover mapping. Two of the first Sentinel-1A images acquired during its ramp-up phase in May and December 2014 over Thuringia in Germany are analysed. 27 hybrid level 2/3 CORINE classes are defined. 17 of these were present at the study site and classified based on a stratified random sample of training pixels from the polygon-eroded CORINE 2006 map. Sentinel-1A logarithmic radar backscatter at HH and HV polarisation (May acquisition), VV and VH polarisation (December acquisition), and the HH image texture are used as input bands to the classification. In addition, a Digital Terrain Model (DTM), a Canopy Height Model (CHM) and slope and aspect maps from the Shuttle Radar Topography Mission (SRTM) are used as input bands to account for geomorphological features of the landscape. In future, elevation data will be delivered for areas with sufficiently high coherence from the Sentinel-1A Interferometric Wide-Swath Mode itself. When augmented by elevation data from radar interferometry, Sentinel-1A is able to discriminate several CORINE land cover classes, making it useful for monitoring of cloud-covered regions. A bistatic Sentinel-1 Convoy mission would enable single-pass interferometric acquisitions without temporal decorrelation.

Mapping hydrological environments in central Amazonia: ground validation and surface model based on SRTM DEM data corrected for deforestation

Abstract. One of the most important freely available digital elevation models (DEMs) for Amazonia is the one obtained by the Shuttle Radar Topography Mission (SRTM). However, since SRTM tends to represent the vegetation surface instead of the ground surface, the broad use of SRTM DEM as a framework for terrain description in Amazonia is hampered by the presence of deforested areas. We present here two data sets: (1) a deforestation-corrected SRTM DEM for the interfluve between the Purus and Madeira rivers, in central Amazonia, which passed through a careful identification of different environments and has deforestation features corrected by a new method of increasing pixel values of the DEM (Rennó, 2009); and (2) a set of 18 hydrological-topographic descriptors based on the corrected SRTM DEM. Deforestation features are related with the opening of an 800 km road in the central part of the interfluve and occupancy of its vicinity. We used topographic profiles from the pristine forest to the deforested feature to evaluate the recovery of the original canopy coverage by minimizing canopy height variation (corrections ranged from 1 to 38 m). The hydrological–topographic description was obtained by the Height Above the Nearest Drainage (HAND) algorithm, which normalizes the terrain elevation (above sea level) by the elevation of the nearest hydrologically connected drainage. The validation of the HAND data set was done by in situ hydrological description of 110 km of walking trails also available in this data set. The new SRTM DEM expands the applicability of SRTM data for landscape modelling; the data sets of hydrological features based on topographic modelling are undoubtedly appropriate for ecological modelling and an important contribution to environmental mapping of Amazonia. The deforestation-corrected SRTM DEM is available at http://ppbio.inpa.gov.br/knb/metacat/naman.318.3/ppbio; the polygons selected for deforestation correction are available at http://ppbio.inpa.gov.br/knb/metacat/naman.317.3/ppbio; the set of hydrological–topographic descriptors is available at http://ppbio.inpa.gov.br/knb/metacat/naman.544.2/ppbio; the environmental description of access trails is available at http://ppbio.inpa.gov.br/knb/metacat/naman.541.2/ppbio; and the limits of deforestation corrections and drainage validation are available at http://ppbio.inpa.gov.br/knb/metacat/liliandias.38.1/ppbio.

SEMI-AUTOMATIC SHIP DETECTION USING PI-SAR-L2 DATA BASED ON RAPID FEATURE DETECTION APPROACH

Synthetic Aperture Radar (SAR) satellite an active sensor offering unique high spatial resolution regardless of weather conditions can operate both day and night time with wide area coverage. Therefore, SAR satellite can be used for monitoring ship on sea surface. This study showed on an alternative method for ship detection of SAR data using Pi-SAR-L2 (L-band, JAXA-Airborne SAR) data. The ship detection method is this study was consisted of eight main stages. After the Pi-SAR data was registered and speckle was filtered, then the land was masked using SRTM-DEM (Shuttle Radar Topography Mission-Digital Elevation Model) data since most ship detectors produced false detections when it applied to land areas. A ship sample image was then selected (cropped). The next step was to detect some unique keypoints of ship sample image using Speeded Up Robust Features (SURF) detector. The maximum distance (‘MaxDist’) of keypoints was also calculated. The same detector was then applied to whole Pi-SAR imagery to detect all possible keypoints. Then, for each detected keypoint, we calculated distance to other keypoint (‘Dist’). If ‘Dist’ was smaller than ‘MaxDist’, then we marked these two (or more) keypoints as neighboring keypoints. If the number of neighbor keypoints was equal or greater than two, finally we marked these keypoints as ‘Detected Ship’ (draw rectangle and show its geographic position). Results showed that our method can detect successfully 32 ‘possible ships’ from Pi-SAR-L2 data acquired on the area of North Sulawesi, Indonesia (August 8, 2012).

Evaluating Information Loss of SRTM DEM Data with Different Grid Sizes

AbstractThe digital elevation products produced by the Shuttle Radar Topography Mission (SRTM) are disseminated with different resolutions. This study investigates the differences in information content between different resolutions. Three 1° cells are selected to represent flat area, moderate terrain, and mountain ranges. All of these cells are located in the continental territory of the United States. The theory of information loss caused by the sampling density is shown with the increasing deviation from the reference in the experiment. The error resulting from bilinear interpolation is also assessed. The experimental result also indicates that if the 1-arcsecond SRTM, digital elevation model (DEM) is released for global coverage, the height accuracy would be improved ∼10% over the 3-arcsecond product.

Application of the inundation area—lake level rating curves constructed from the SRTM DEM to retrieving lake levels from satellite measured inundation areas

Remote sensing technology has great potential for measuring lake inundation areas and lake levels, and providing important lake water quantity and quality information which can be used for improving our understanding of climate change impacts on the global water cycle, and assessing the influence of the projected future climate change on the global water resources. One remote sensing approach is to estimate lake level from satellite measured inundation area based on the inundation area—lake level rating (IALLR) curves. However, this approach is not easy to implement because of a lack of data for constructing the IALLR curves. In this study, an innovative and robust approach to construct the IALLR curves from the digital elevation model (DEM) data collected during the Shuttle Radar Topography Mission (SRTM) was developed and tested. It was shown that the IALLR curves derived from the SRTM DEM data could be used to retrieve lake level from satellite measured inundation area. Applying the constructed IALLR curve to the estimated inundation areas from 16 Landsat Thematic Mapper (TM) images, 16 lake levels of Lake Champlain in Vermont were obtained. The root mean square error (RMSE) of the estimated lake levels compared to the observed water levels at the U.S. Geological Survey (USGS) gauging station (04294500) at Burlington, Vermont is about 0.12m.

Limitation of 90 m SRTM DEM in drainage network delineation using D8 method—a case study in flat terrain of Bangladesh

Bangladesh is the deltaic flood plain located in the lower ridge of the Ganges Brahmaputra and Meghna basins. The country is very flat having 40% of its landmass up to 10 m above the mean sea level. Shuttle Radar Topography Mission (SRTM) 90 m, i.e., 3-arc second digital elevation model (DEM) is being widely used to delineate river network and to extract catchment information using hydrology tool of ArcGIS. The hydrology tool uses the D8 method for extraction of drainage pattern. The study was carried out to find the limitation and suitability of 90 m SRTM DEM data in flat terrains especially in Bangladesh using ArcGIS. Twelve catchments of varying geomorphology were chosen from five hydrological zones of Bangladesh. Basin characteristics such as bifurcation ratio, drainage density, and channel slope of the catchments were estimated and analyzed to evaluate the suitability of 90 m SRTM DEM. The delineated catchments of slope 1:3,600 or more flat shows large deviation in river network alignment when compared with the digital river network developed by Bangladesh Water Development Board and with Google Earth’s images. The catchments having slope 1:2,850 and more steep were delineated correctly. The conclusion could not be established between slopes 1:2,850 and 1:3,600. The study also revealed that the catchment characteristics other than the slope have no effect on river network delineation.

Fault growth and propagation during incipient continental rifting: Insights from a combined aeromagnetic and Shuttle Radar Topography Mission digital elevation model investigation of the Okavango Rift Zone, northwest Botswana

Digital Elevation Models (DEM) extracted from the Shuttle Radar Topography Mission (SRTM) data and high‐resolution aeromagnetic data are used to characterize the growth and propagation of faults associated with the early stages of continental extension in the Okavango Rift Zone (ORZ), northwest Botswana. Significant differences in the height of fault scarps and the throws across the faults in the basement indicate extended fault histories accompanied by sediment accumulation within the rift graben. Faults in the center of the rift either lack topographic expressions or are interpreted to have become inactive, or have large throws and small scarp heights indicating waning activity. Faults on the outer margins of the rift exhibit either (1) large throws or significant scarp heights and are considered older and active or (2) throws and scarp heights that are in closer agreement and are considered young and active. Fault linkages between major fault systems through a process of “fault piracy” have combined to establish an immature border fault for the ORZ. Thus, in addition to growing in length (by along‐axis linkage of segments), the rift is also growing in width (by transferring motion to younger faults along the outer margins while abandoning older faults in the middle). Finally, utilization of preexisting zones of weakness allowed the development of very long faults (>100 km) at a very early stage of continental rifting, explaining the apparent paradox between the fault length versus throw for this young rift. This study clearly demonstrates that the integration of the SRTM DEM and aeromagnetic data provides a 3‐D view of the faults and fault systems, providing new insight into fault growth and propagation during the nascent stages of continental rifting.

Evaluation of ASTER and SRTM DEM data for lahar modeling: A case study on lahars from Popocatépetl Volcano, Mexico

Lahars are among the most serious and far-reaching volcanic hazards. In regions with potential interactions of lahars with populated areas and human structures the assessment of the related hazards is crucial for undertaking appropriate mitigating actions and reduce the associated risks. Modeling of lahars has become an important tool in such assessments, in particular where the geologic record of past events is insufficient. Mass-flow modeling strongly relies on digital terrain data. Availability of digital elevation models (DEMs), however, is often limited and thus an obstacle to lahar modeling. Remote-sensing technology has now opened new perspectives in generating DEMs. In this study, we evaluate the feasibility of DEMs derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) for lahar modeling on Popocatépetl Volcano, Mexico. Two GIS-based models are used for lahar modeling, LAHARZ and a flow-routing-based debris-flow model (modified single-flow direction model, MSF), both predicting areas potentially affected by lahars. Results of the lahar modeling show that both the ASTER and SRTM DEMs are basically suitable for use with LAHARZ and MSF. Flow-path prediction is found to be more reliable with SRTM data, though with a coarser spatial resolution. Errors of the ASTER DEM affecting the prediction of flow paths due to the sensor geometry are associated with deeply incised gorges with north-facing slopes. LAHARZ is more sensitive to errors of the ASTER DEM than the MSF model. Lahar modeling with the ASTER DEM results in a more finely spaced predicted inundation area but does not add any significant information in comparison with the SRTM DEM. Lahars at Popocatépetl are modeled with volumes of 1 × 10 5 to 8 × 10 6 m 3 based on ice-melt scenarios of the glaciers on top of the volcano and data on recent and historical lahar events. As regards recently observed lahars, the travel distance of lahars of corresponding volume modeled with LAHARZ falls short by 2 to 4 km. An important finding is that the travel distance of potential lahar events modeled with LAHARZ may differ by about 2 km when using SRTM or ASTER data because of varying lateral flow-volume distribution. As a consequence, verification and sensitivity analysis of the DEM is fundamental to deriving hazard maps from predicted modeled inundation areas. Because of the global coverage of this type of remote-sensing data, the conclusion that both SRTM and ASTER-derived DEMs are feasible for lahar modeling opens a wide field of application in volcanic-hazards studies.

The Shuttle Radar Topography Mission—A New Source of Near-Global Digital Elevation Data

The Shuttle Radar Topography Mission (SRTM) has generated a homogeneous near-global digital elevation model (DEM) of the Earth using single-pass radar interferometry. The crew of Space Shuttle Endeavour (STS-99) operated the modified dual-antenna synthetic aperture radar systems for 11 days in February 2000. SRTM acquired both C-band and X-band synthetic aperture radar data, collecting 3D data using a 60-metre mast extending from the shuttle payload bay, containing additional C-band and X-band receiver antennas.SRTM DEM data have a horizontal resolution of 1 arc second (30 m at the equator) and vertical resolution of 10 m (C-band radar). SRTM-1 (1 arc second) data are available for US territories only, with subsampled SRTM-3 (3 arc second) data provided for the rest of the world. The USGS is responsible for archiving the data, with 3 arc second data being made freely available on a continent-by-continent basis. All data processing was completed in July 2004. Comparison of SRTM DEM data with older GTOPO and altimetric DEMs shows a significant improvement in horizontal and/or vertical resolution, similar to that achieved by ASTER. The SRTM DEM data provide a useful new resource, especially in areas where limited topographic data are available.

Automated georeferencing and orthorectification of Amazon basin-wide SAR mosaics using SRTM DEM data

Frequently large synthetic aperture radar (SAR) mosaics are not precisely georeferenced because topographic distortions are not removed during the mosaicking process due to the lack of adequate digital elevation models (DEMs). The Shuttle Radar Topography Mission (SRTM) has recently provided high-resolution DEM data with nearly global coverage and makes it possible to rectify SAR mosaics. Though techniques are available for rectifying individual scenes of SAR imagery using DEM data, these methods encounter difficulties when rectifying SAR mosaics because abrupt geometric discontinuities occur in SAR mosaics at scene boundaries. This paper introduces an automated method to removing topographic distortions from SAR mosaics and producing orthorectified mosaics, without accessing original SAR images. The procedures include SAR image simulation from DEMs, two-staged image matching between SAR mosaics and the simulated image, automated tie-point derivation and screening, piecewise image rectification for localized adjustment, and production of orthorectified mosaics. The method is used to orthorectify both high-water and low-water Global Rain Forest Mapping project SAR mosaics covering the entire Amazon basin. Validation results show that one-pixel (i.e., 92 m) positioning accuracy (root mean square error) was achieved in both cases, compared to 14-16 pixel errors (i.e., 1288-1472 m) of the original mosaics.

The Shuttle Radar Topography Mission–a new source of near-global digital elevation data

The Shuttle Radar Topography Mission (SRTM) has generated a homogeneous near-global digital elevation model (DEM) of the Earth using single-pass radar interferometry. The crew of Space Shuttle Endeavour (STS-99) operated the modified dual-antenna synthetic aperture radar systems for 11 days in February 2000. SRTM acquired both C-band and X-band synthetic aperture radar data, collecting 3D data using a 60-metre mast extending from the shuttle payload bay, containing additional C-band and X-band receiver antennas. SRTM DEM data have a horizontal resolution of 1 arc second (30 m at the equator) and vertical resolution of 10 m (C-band radar). SRTM-1 (1 arc second) data are available for US territories only, with subsampled SRTM-3 (3 arc second) data provided for the rest of the world. The USGS is responsible for archiving the data, with 3 arc second data being made freely available on a continent-by-continent basis. All data processing was completed in July 2004. Comparison of SRTM DEM data with older GTOPO and altimetric DEMs shows a significant improvement in horizontal and/or vertical resolution, similar to that achieved by ASTER. The SRTM DEM data provide a useful new resource, especially in areas where limited topographic data are available.